crop in opencv using python

edit

the images used in python are plain numpy arrays. you can get any subrect with a range operation like:

   imsub = img[ ymin:ymax, xmin:xmax ]

so, for a 640x480 image:

   tl = img[:240, :320]
   tr = img[:240, 320:]
   bl = img[240:, :320]
   br = img[240:, 320:]